If you meant that you had the LMDE Xfce installed, and you added MATE to it, then in fact you of course added MATE programs. The GNOME 3 programs were already there, as part of LMDE Xfce (of which most programs are from GNOME 3). Installing MATE would have installed MATE programs.

Having cleared that up, which ones do you want to remove now? The MATE programs, or the GNOME 3 programs that came with LMDE Xfce?